Single-wafer rapid thermal processing (RTP) is a versatile technique for fabrication of very-large-scale integrated (VLSI) and ultra-large-scale integrated (ULSI) circuits. Single-wafer RTP combines low thermal mass, photon-assisted, rapid wafer heating with reactive ambient semiconductor device processing. Both the wafer temperature and the process environment can be quickly controlled and, as a result, it is possible to optimize each fabrication step to improve the overall electrical performance of the circuits.
RTP is one form of single-wafer semiconductor wafer processing that can provide improved wafer-to-wafer process repeatability in single-wafer, lamp-heated, thermal processing reactors. Numerous semiconductor fabrication technologies may use RTP techniques, including thermal oxidation, nitridation, implant activation, dopant diffusion, and different types of thermal anneals. Chemical-vapor deposition (CVD) is another type of device fabrication process that can benefit from RTP in single-wafer reactors. For example, CVD processes using advanced RTP techniques to form dielectrics (e.g., oxides and nitrides), semiconductors (e.g., amorphous silicon and polysilicon), and conductors (e.g., aluminum, copper, tungsten, and titanium nitride) have significant potentials in VLSI and ULSI device fabrication.
FIG. 1 illustrates a known RTP system 20 for semiconductor wafer processing. The system 20 of FIG. 1 uses two banks 22 and 24 of lamps 26 which are arranged in orthagonal or cross directions. The lamps are placed outside the reactor chamber's quartz windows 30. Reflectors 32 and 34 are placed behind lamp banks 22 and 24, respectively. Quartz susceptor 36 holds semiconductor wafer 38, and semiconductor wafer 38 front and back surfaces face lamp banks 22 and 24. Relative power to each lamp 26 may be set and overall power may be controlled to maintain desired temperature by computer lamp controller 40. Computer lamp controller 40 receives temperature signal input from pyrometer 42. Rotary pump 44 vacuum manifold and gas manifold 46 maintain process chamber environment 28 for various processes.
The conventional type of RTP system such as that of FIG. 1, may provide generally uniform wafer heating during some steady-state conditions. However, the known RTP systems cannot provide uniform wafer heating over a wide range of temperatures and during both the transient and steady-state conditions. The resultant wafer temperature nonuniformities can result in process nonuniformities and possibly slip dislocations. In fact, the most critical problems with commercial RTP systems are process nonuniformities caused by the steady-state and transient temperature nonuniformities.
Some existing tungsten-halogen lamp-heated RTP systems such as that of the FIG. 1, employ two crossed banks of linear tungsten-halogen lamps. While this configuration may provide a limited capability for steady-state temperature uniformity control, it does not provide complete uniformity adjustment and does not provide cylindrical symmetry consistent with the circular shape of semiconductor wafer 38. Moreover, the design of FIG. 1 provides no reliable and accurate measure of wafer 38 temperature. In addition, this type of RTP system does not provide any RF plasma capability for in-situ plasma processing applications.
The RTP temperature control and process nonuniformity problems are particularly manifested in the form of localized wafer edge cooling due to excessive heat losses by radiation and gas cooling. FIG. 2 shows a qualitative plot of wafer temperature versus radial position that demonstrates the edge problem. In FIG. 2, the vertical axis represents wafer temperature and the horizontal axis has an origin at the center C and range in equal directions between -R and +R at the edge points of semiconductor wafer 38. According to FIG. 2, at the center C, semiconductor wafer 38 may achieve a temperature T.sub.c. Throughout a significant portion of the radial distance from C to the edge of semiconductor wafer 38, the temperature can be made approximately equal to T.sub.c. Close to the edge, however, the temperature usually drops. The arc labeled "edge cooling" indicates that at the -R and +R edge points on semiconductor wafer 38, semiconductor wafer 38 temperature falls to the edge cooled level of T.sub.e. The amount of center-to-edge temperature variation may be a few degrees up to 10's of degrees C.
The extent of the temperature nonuniformity problem depends on the target wafer temperature and the RTP system design as well as process parameters such as chamber pressure. For a given RTP lamp, the wafer temperature nonuniformity may also depend on the details of the thermal cycle. The transient thermal nonuniformity is, in general, different from the steady-state temperature nonuniformity. If the lamp module for heating semiconductor wafer employs a single high-power arc lamp, there is basically no flexibility for real-time control or optimization of wafer temperature uniformity by changing or adjusting the optical flux distribution on the wafer. In commercial RTP systems with tungsten-halogen lamps such as that in FIG. 1, there is no practical way to adjustably control the transient and steady-state temperature uniformity profiles over the entire wafer area. High-temperature RTP techniques particularly exacerbate this problem. For example, in some applications fabrication temperatures may reach as high as 1100.degree. C. and good wafer temperature uniformity is required in order to avoid slip dislocations and process nonuniformities.
Another semiconductor device fabrication technique that has many applications is known as "plasma-enhanced processing." In plasma-enhanced processing, a substantially ionized gas, usually produced by a radio-frequency (RF) or microwave electromagnetic gas discharge, generates a mixture of ions, electrons, and excited neutral species, which may react to deposit or etch various material layers on semiconductor substrates in a wafer processing reactor. Plasma-enhanced chemical-vapor deposition (PECVD) is an example of a widely-used plasma-enhanced semiconductor device fabrication process. PECVD uses the activated neutrals and ions in the plasma to deposit material layers at high rates and lower temperatures on a semiconductor substrate.
Various PECVD applications for plasma-enhanced processing and semiconductor device manufacturing include deposition of amorphous silicon, polysilicon, tungsten, aluminum, and dielectric layers. Plasma-enhanced metal-organic chemical-vapor deposition processes (PEMOCVD) also are useful for high-rate deposition of material layers such as aluminum and copper films for device interconnection applications. Plasma-enhanced deposition techniques can also be used for planarized interlevel dielectric formation. Additional applications of PECVD techniques include low-temperature epitaxial silicon growth as well as diamond thin films.
If it were possible to concurrently and/or sequentially perform plasma-enhanced processing together with lamp-heated processing (RTP) in the same chamber without having to reconfigure the fabrication reactor, numerous semiconductor device fabrication processes could be materially enhanced. For example, such a system would provide for rapid thermal chemical-vapor deposition (RTCVD) of various material layers with in-situ process chamber cleaning. There is no known RTP system that accomplishes these objectives in a flexible manner.
As a result of the above, there is a need for a method and apparatus to provide both steady-state and transient semiconductor device fabrication process uniformity for rapid thermal processing (RTP) applications.
There is a need for a device that permits accurate real-time measurement of temperature across the entire semiconductor wafer.
There is a need for a method and apparatus that allows semiconductor device fabrication process control flexibility based on the particular application as well as real-time temperature readings of the semiconductor wafer temperature and its uniformity.
Moreover, there is a need for a semiconductor device fabrication apparatus that permits flexible and uniform wafer processing for various thermal processing applications.
There is yet the need for an apparatus for plasma generation within the semiconductor wafer processing chamber that is both reliable and controllable.
There is the further need for a method and apparatus to support coordinated plasma generation for plasmaenhanced semiconductor device fabrication processes and lamp-heated rapid thermal processes.